1. Field of the Invention
This invention relates generally to the field of repair of aircraft windshields incorporating laminated glass plies with polymeric laminating film interlayers. More particularly, the invention relates to a refurbishment method incorporating removal of a glass face ply, removing material from the polymeric laminating interlayer by machining, preparing the exposed surface of the polymeric interlayer, and rebonding additional polymeric material and a new face ply.
2. Prior Art
Aircraft windshields typically comprise a laminated structure consisting of layers of glass, acrylic or polycarbonate plastics, or combinations thereof bonded together by interlayers of a polymeric bonding material. This laminated structure provides the high strength at reduced weight necessary for use in aircraft. The environment to which such laminated windshields are exposed is severe and the outer surface, known as the face ply, is often damaged due to particulate impacts, scratching or bond failures (delaminations) at interlayer interfaces and/or electrical faults in anti-icing heater coatings caused by cyclical thermally and mechanically induced stresses, moisture ingress and bond deterioration. Such damage is the chief cause for removal of front windshields, and almost invariably occurs at the inner surface of the outermost ply and/or within the interlayer adjacent thereto.
Replacement of windshield assemblies is expensive, consequently refurbishment of such windshields is desirable if such refurbishment can be accomplished at less than replacement cost. Aircraft windshields incorporating a glass face ply laminated to acrylic structural plies by means of polyvinyl butyral (PVB) interlayers are known as glass/plastic, or composite laminate windshields. Such glass/plastic laminate windshields typically employ a PVB interlayer which is approximately 0.1 inches thick. Damage of the face ply or bond interface between the face ply and the interlayer is typically refurbished in such glass/plastic laminate windshields by removing the windshield from the aircraft, removing the face ply and pealing the entire interlayer from the acrylic structural layer. A new glass face ply is then bonded to the acrylic employing a new interlayer.
Windshields incorporating a glass face ply bonded to glass structural layers in a laminate are typically called glass/glass, or "all glass" laminate windshields. All glass laminate windshields employ a PVB interlayer between the glass face ply and first glass structural ply that is typically thicker than in a glass/plastic laminate windshield and is usually approximately 0.2 inches to 0.4 inches in thickness. The PVB layer typically employs various embedded electrical components such as cabling for heater elements on the glass plies for anti-ice/defog on the windshield and sensor elements for control of the heaters. The structure of all glass laminate windshields has typically precluded cost effective refurbishment of the windshields, and damaged windshields are typically removed and discarded to be replaced with new components. All glass laminate windshields typically have not been repairable due the superior bond strength of the glass to the interlayer which precludes peeling of the interlayer from the glass which is the typical repair approach for glass/plastic laminate windshields. In addition, greater thickness of the glass and the presence of the anti-ice/defog inserts further precludes peeling of the interlayer.
There is a need in the art therefore for a simple and economical process for refurbishing aircraft windshields which incorporate a glass face ply laminated to glass structural plies through PVB interlayers, while maintaining optical requirements of the windshield. The present invention provides a process and tool for accomplishing such refurbishment at significantly reduced cost while maintaining satisfactory optical properties for the refurbished windshield.